The present invention concerns a means for clearing the blocked reject end of a vortex purifier without interrupting normal operation of the vortex purifier.
Vortex purifiers (also hydro or liquid cyclones) are used mainly in the cellulose and paper industry for purifying fibre suspensions of impurities, such as sand, bark and splinter particles and metal particles. The fibre suspension to be purified is supplied under pressure tangentially into the vortex purifier, whereby the mass is set into rapid rotation, the materials in the fibre suspension having different specific gravities in shape being separated onto circles with different radii by effect of the centrifugal force created by said rotation. Heavier constituents, such as sand, become separated on the outer circumference and move towards the exit aperture with comparatively small diameter in the tip of the sorter cone. The purified fibre suspension, the accept flow, exits around the vacuum core that is established in the vortex purifier, into a coaxial exit tube at the accept end of the vortex purifier.
Since vortex purifiers become more efficient in removing small foreign particles when the diameter of the vortex purifier is reduced, the industry has adopted the practice of using a greater number of vortex purifiers with smaller dimensions. The problem, particularly in present small vortex purifiers, is blocking of the reject exit aperture. Such blocking is caused by over-sized particles and by slowly accumulating deposits in the vicinity of the exit aperture. When the reject aperture becomes blocked, the sorting ability of the vortex purifier ceases and the impurities are entrained with the accept flow to subsequent process steps.
Solutions of this problem known in the art are of many kinds as to their characteristic features. The oldest vortex purifiers had to be partly dismantled when clearing the blocked reject exit aperture. Other designs have included reject exit apertures of variable size, water or compressed air jets directed into the exit aperture, valves placed at the exit apertures of the apparatus, and combinations of these.
Said designs are characterized by the use of force or pressure for disrupting the blockage, whereat impurities tend to be entrained with the accept flow and to discharge through the accept tube of the vortex purifier, thereby contaminating the accept mass. The valve designs are fixed in nature and become expensive because the reject end of each vortex purifier must be provided with a valve.
In the Finnish Pat. No. 65458 is disclosed a well-functioning design for clearing the reject end of a vortex purifier. Therein, to the reject end is connected a separate cleaning means with which the bottom plug of the purifier is opened. The reject flow is conducted through an exit aperture in said means to the desired location without interfering with the operation of the purifier and without contaminating the accept flow.